Window Contamination Research Articles

Oxygen K-edge X-ray absorption spectra of liquids with minimization of window contamination.

Oxygen K-edge X-ray absorption spectroscopy is used routinely to study a range of solid materials. However, liquid samples are studied less frequently at the oxygen K-edge due to the combined challenges of high-vacuum conditions and oxygen contamination of window materials. A modular sample holder design with a twist-seal sample containment system that provides a simple method to encapsulate liquid samples under high-vacuum conditions is presented. This work shows that pure silicon nitride windows have lower oxygen contamination than both diamond- and silicon-rich nitride windows, that the levels of oxygen contamination are related to the age of the windows, and provides a protocol for minimizing the background oxygen contamination. Acid-washed 100 nm-thick silicon nitride windows were found to give good quality oxygen K-edge data on dilute liquid samples.

Study on the pack rolling process factor of Ti-6Al-4V alloy

Pack rolling method is preferred to conventional rolling method to process thin sheets or foils out of titanium alloys because of their relatively narrow processing window and possible surface contamination during the elevated temperature processing. In this paper, the core sheets of 5mm thick with equiaxed alpha + transformed beta structure were encapsulated in mild steel cover material and hot rolled in a four high reversing hot rolling mill. The following results were obtained; The optimal pack assembly condition and pack rolling process factor were produced. The effect that the difference in deformation resistance of cover material and core material in pack rolling has been considered. The S45C mild steel is the most suitable for the cover material. The cover material is subjected to the same rolling process as the core material when the initial core and total thickness ratio is 0.3. The reduction in pack rolling should be selected in the range of 20% to 25% to produce flat sheet. Tensile properties of the pack rolled sheet are isotropic in both RD and TD rolling direction which meet the requirements of the standard AMS4911.

Experimental investigation of surface adhesion of Titan analog materials: Mitigation by dust-repellent coatings

We report an experimental investigation of organic Titan regolith simulant interactions with transparent surfaces. In the absence of prior triboelectrification of the particles and surface, the area coverage of sprinkled particles increases with increasing substrate surface energy, as expected. Bare sapphire, sapphire coated with indium tin oxide (ITO), and sapphire coated with ITO and fluorosilane collected 20%, 10%, and 5% particles, respectively. Under turbulent conditions that promote triboelectric charging, the adhesion of Titan regolith analogs is enhanced. Bare sapphire occluded by more than 60% in some cases. However, conductive ITO generally reduced the area coverage below 10% when electrically grounded, and the fluorosilane treatment reduced it slightly further. The surface coatings tested, and anti-static measures more generally, therefore provide significant mitigation of optical window contamination.

Concentration measurements by intracavity laser absorption spectroscopy for the case of strongly overlapped spectra

The feasibility of fiber laser intracavity absorption spectroscopy (FLICAS) for accurate measurement of pressure and concentration of CO and $$\hbox {CO}_2$$ at elevated pressures (up to 6.5 atm) was studied. FLICAS is a very sensitive absorption spectroscopy method which allows for simultaneous measurement of several species even in harsh environment, since it is not sensitive to broadband optical losses caused by particle scattering and absorption, optical window contamination, etc. However, the wings of spectral lines can overlap at elevated pressures, resulting in broadband absorption which is not monitored by FLICAS. It makes the direct evaluation of baseline challenging. Nevertheless, fitting the lineshapes of individual lines using the HITRAN database allows for recovering of the baseline position and shape in some cases. The CO and $$\hbox {CO}_2$$ spectra were studied under controlled conditions in the spectral range of 6350–6385 cm $$^{-1}$$ and processed by custom LabVIEW code to take into account the overlapping line effect. This procedure allows for accurate determination of the pressure and the CO concentration at least up to 6.5 atm. More dense and line-rich $$\hbox {CO}_2$$ spectrum allows correct pressure evaluation up to 6.5 atm, albeit with higher uncertainty. Accurate measurements of the $$\hbox {CO}_2$$ concentration are possible only up to about 4 atm.

Gradient heating protocol for a diode-pumped alkali laser

A diode-pumped alkali laser (DPAL) has gained rapid development in the recent years. Until now, the structure with single heater has been widely utilized to adjust the temperature of an alkali vapor cell in most of the literatures about DPALs. However, for an end-pumped DPAL using single heater, most pump energy is absorbed by the gain media near the entrance cell window because of the large absorption cross section of atomic alkali. As a result, the temperature in the pumping area around the entrance window will go up rapidly, especially in a case of high pumping density. The temperature rise would bring about some negative influences such as thermal effects and variations in population density. In addition, light scattering and window contamination aroused by the chemical reaction between the alkali vapor and the buffer gas will also affect the output performance of a DPAL system. To find a solution to these problems, we propose a gradient heating approach in which several heaters are tandem-set along the optical axis to anneal an alkali vapor cell. The temperature at the entrance window is adjusted to be lower than that of the other side. By using this novel scheme, one can not only achieve a homogeneous absorption of the pump energy along the cell axis, but also decrease the possibility of the window damage in a DPAL configuration. The theoretical simulation of the laser output features has been carried out for a configuration of multiple heaters. Additionally, the DPAL output performance under different gradient temperatures is also discussed in this paper. The conclusions might be helpful for development of a high-powered and high-beam-quality DPAL.

Integrating cavity based gas cells: a multibeam compensation scheme for pathlength variation.

We present a four beam ratiometric setup for an integrating sphere based gas cell, which can correct for changes in pathlength due to sphere wall contamination. This allows for the gas absorption coefficient to be determined continuously without needing to recalibrate the setup. We demonstrate the technique experimentally, measuring methane gas at 1651nm. For example, contamination covering 1.2% of the sphere wall resulted in an uncompensated error in gas absorption coefficient of ≈41%. With the ratiometric scheme, this error was reduced to ≈2%. Potential limitations of the technique, due to subsequent deviations from mathematical assumptions are discussed, including severe sphere window contamination.

Correction of temperature errors due to the unknown effect of window transmission on ratio pyrometers using an in situ calibration standard

Ratio pyrometers are widely used for non contact temperature measurement in situations where non-blackbody conditions exist. A high temperature fixed-point cell based on rhenium–carbon alloy was used to characterise the effect of window contamination based on the simplest assumption that graybody conditions existed. A visible-near IR spectrometer was used to mimic the behaviour of a ratio pyrometer. The deposition of particulate contamination on clean glass windows was found to substantially change the indicated temperature. This change is liable to be unpredictable. The use of an in-process reference fixed-point cell was tested and found to give potential for significant reduction of errors across a wide temperature range.

Window contamination on Expose-R

AbstractExpose is a multi-user instrument for astrobiological and astrochemical experiments in space. Installed at the outer surface of the International Space Station, it enables investigators to study the impact of the open space environment on biological and biochemical test samples. Two Expose missions have been completed so far, designated as Expose-E (Rabbow et al. 2012) and Expose-R (Rabbow et al. this issue). One of the space-unique environmental factors offered by Expose is full-spectrum, ultraviolet (UV)-rich electromagnetic radiation from the Sun. This paper describes and analyses how on Expose-R, access of the test samples to Solar radiation degraded during space exposure in an unpredicted way. Several windows in front of the Sun-exposed test samples acquired a brown shade, resulting in a reduced transparency in visible light, UV and vacuum UV (VUV). Post-flight investigations revealed the discolouration to be caused by a homogenous film of cross-linked organic polymers at the inside of the windows. The chemical signature varied per sample carrier. No such films were found on windows from sealed, pressurized compartments, or on windows that had been kept out of the Sun. This suggests that volatile compounds originating from the interior of the Expose facility were cross-linked and photo-fixed by Solar irradiation at the rear side of the windows. The origin of the volatiles was not fully identified; most probably there was a variety of sources involved including the biological test samples, adhesives, plastics and printed circuit boards. The outer surface of the windows (pointing into space) was chemically impacted as well, with a probable effect on the transparency in VUV. The reported analysis of the window contamination on Expose-R is expected to help the interpretation of the scientific results and offers possibilities to mitigate this problem on future missions – in particular Expose-R2, the direct successor of Expose-R.

Ceilometer calibration for retrieval of aerosol optical properties

Ceilometers are durable compact backscatter lidars widely used to detect cloud base height. They are also useful for measuring aerosols. We introduced a ceilometer (CL51) for observing dust in a source region in Mongolia. For retrieving aerosol profiles with a backscatter lidar, the molecular backscatter signal in the aerosol free heights or system constant of the lidar is required. Although the system constant of the ceilometer is calibrated by the manufacturer, it is not necessarily accurate enough for the aerosol retrieval. We determined a correction factor, which is defined as the ratio of true attenuated backscattering coefficient to the measured attenuated backscattering coefficient, for the CL51 ceilometer using a dual-wavelength Mie-scattering lidar in Tsukuba, Japan before moving the ceilometer to Dalanzadgad, Mongolia. The correction factor determined by minimizing the difference between the ceilometer and lidar backscattering coefficients was approximately 1.2±0.1. Applying the correction to the CL51 signals, the aerosol optical depth (AOD) agreed well with the sky-radiometer AOD during the observation period (13–17 February 2013) in Tsukuba (9×10−3 of mean square error). After moving the ceilometer to Dalanzadgad, however, the AOD observed with the CL51 (calibrated by the correction factor determined in Tsukuba) was approximately 60% of the AErosol RObotic NETwork (AERONET) sun photometer AOD. The possible causes of the lower AOD results are as follows: (1) the limited height range of extinction integration (<3km); (2) change in the correction factor during the ceilometer transportation or with the window contamination in Mongolia. In both cases, on-site calibrations by dual-wavelength lidar are needed. As an alternative method, we showed that the backward inversion method was useful for retrieving extinction coefficients if the AOD was larger than 1.5. This retrieval method does not require the system constant and molecular backscatter signals, and can be applied to severe dust and air pollution aerosol cases in East Asia.

Overestimation of Downward Air-Sea Eddy CO&lt;sub&gt;2&lt;/sub&gt; Flux Due to Optical Window Contamination of Open-Path Gas Analyzer

Open-path eddy-covariance CO2 flux over the ocean have been reported to be much larger in magnitude than the estimated bulk CO2 flux, and optical window contamination of the open-path gas analyzers has been reported as the cause of the overestimations. During an on-board experiment over the ocean, we manually cleaned the optical window and directly compared CO2 output signal before and after the window cleaning. It is found that both of the CO2 fluctuation amplitude and correlation coefficient between vertical wind velocity and CO2 mixing ratio have apparently increased, then resulting in the downward CO2 flux overestimation when the optical window contamination accumulate. These apparent increases were reset after the manual window cleaning. Correlation coefficients between CO2 and H2O output signals, which represent cross-sensitivity between CO2 and H2O, can be useful indicators of optical window contamination of the open-path gas analyzer.

Experimental evaluation of water vapour cross-sensitivity for accurate eddy covariance measurement of CO2 flux using open-path CO2/H2O gas analysers

Non-dispersive infrared CO2/H2O gas analysers produce erroneous CO2 outputs when CO2 is measured in humid air, unless a correction for water vapour cross-sensitivity is applied. Spectroscopic cross-sensitivities arising from direct absorption interference and from the pressure broadening effect are significant in CO2 flux measurements by the eddy covariance technique using open-path gas analysers over the ocean, as opposed to land-surface measurements, where CO2 fluxes are orders of magnitude larger. In this study, a widely used analyser with manufacturer-determined correction coefficients for both cross-sensitivities was tested by laboratory experiments. Our results showed that the correction coefficient for direct absorption interference was not optimised to calculate CO2 flux accurately, and that the correction coefficient for the pressure broadening caused overestimation of the CO2 mixing ratio flux in the same direction as the water vapour flux. Overestimations of open-path eddy covariance measurements of upward CO2 fluxes in previous ocean observations probably resulted from inaccuracies in both of these correction coefficients. We also found that slight changes in spectroscopic cross-sensitivities due to contamination of the analyser's optical windows by sea salt caused a low bias in CO2 outputs with increasing H2O; however, this contamination effect was not always observed in repeated tests under different contamination conditions. We suggest that previously proposed methods for correcting the effect of optical window contamination is of limited value and that measurement of small CO2 fluxes by the open-path eddy covariance technique over the ocean should be performed after confirming the spectroscopic cross-sensitivity and ensuring that the optical windows are as clean as possible.

High Refractive Index Fluid Evaluations at 193nm: Fluid Lifetime and Fluid/Resist Interaction Studies

We report on recent studies on two of our leading fluid candidates for high index immersion lithography, designated IF132 and IF169. The most recent fluid radiation durability results are discussed, leading us to define two important parameters, the fluid lifetime factor and the clean window dose related to suppression of window contamination through use of active recycle technology. Results of fluid-resist interactions, with water and high index fluids on four commercial resists, will be shown. These experiments include PAG leaching and contact angle measurements, resist profile and thickness changes due to pre- and post-exposure fluid contact, residues and defects from the fluid and from resist contact, and 36 nm hp imaging on an immersion interference printer.

Comparison of Image Quality of Different Iodine Isotopes (I-123, I-124, and I-131)

I-131 is a frequently used isotope for radionuclide therapy. This technique for cancer treatment requires a pre-therapeutic dosimetric study. The latter is usually performed (for this radionuclide) by directly imaging the uptake of the therapeutic radionuclide in the body or by replacing it by one of its isotopes, which are more suitable for imaging. This study aimed to compare the image quality that can be achieved by three iodine isotopes: I-131 and I-123 for single-photon emission computed tomography imaging, and I-124 for positron emission tomography imaging. The imaging characteristics of each isotope were investigated by simulated data. Their spectrums, point-spread functions, and contrast-recovery curves were drawn and compared. I-131 was imaged with a high-energy all-purpose (HEAP) collimator, whereas two collimators were compared for I-123: low-energy high-resolution (LEHR) and medium energy (ME). No mechanical collimation was used for I-124. The influence of small high-energy peaks (>0.1%) on the main energy window contamination were evaluated. Furthermore, the effect of a scattering medium was investigated and the triple energy window (TEW) correction was used for spectral-based scatter correction. Results showed that I-123 gave the best results with a LEHR collimator when the scatter correction was applied. Without correction, the ME collimator reduced the effects of high-energy contamination. I-131 offered the worst results. This can be explained by the large amount of septal penetration from the photopeak and by the collimator, which gave a low spatial resolution. I-124 gave the best imaging properties owing to its electronic collimation (high sensitivity) and a short coincidence time window.

An optical IR-source and CO/sub 2/-chamber system for CO/sub 2/ measurements

A new silicon IR source and CO/sub 2/-chamber system for measurement of CO/sub 2/ concentration is presented. The micromachined IR-source, which consists of four groups of polysilicon filaments coated with silicon nitride suspended across a KOH-etched cavity, is used to generate two switched sample and beams. The electrically modulated sources present a modulation time of 10 ms and a power consumption of 1 W. The CO/sub 2/ chambers, placed beneath the reference sources, are used to produce a reference beam for long term stability and compensation against cuvette window contamination. They consist of 1-mm-deep micromachined cavities in which CO/sub 2/ is encapsulated during an overpressure anodic bonding procedure. Silicon dioxide is used as an antireflective coating to optimize the filter's optical characteristics. Numerical simulations of the filters are presented and show good agreement with the measurements. The IR sources and the CO/sub 2/ filters are both fabricated at wafer level. Using the presented IR-sensor system, measurements with a 9-mm-wide test channel show high CO/sub 2/-sensitivity for CO/sub 2/ concentrations between 0 and 10% confirming that the stringent requirements for this respirator application can be fulfilled.

自動溶接ロボット用視覚センサの実用化研究 １ 視覚センサの開先形状検出方法に関する検討

It is necessary to develop excellent sensors in order to improve the automation or the artificial intelligence of the welding operation.Laser visual sensors are designed to recognize the configuration or debect the position of a weld by irradiating a slit light on to the weld joint, receiving the light with a CCD camera, and then converting the two dimensional information into three dimensional information by using image processing.The visual sensors for the welding robot must be free from the influence of welding process disturbances, such as light, heat, spatter and fumes.This paper deals with optical component arrangements and image processing algorithms. The optical component of a sensor head helps to avoid optical window contamination caused by spatters or fumes. The image processor can process image data very quickly and accurately, even if the welding arc light illuminates the surface of the workpiece. The accuracy of detecting the position is within ±0.2 mm.

電子サイクロトロン共鳴加熱プラズマを用いたリニアスパッタリング装置の作動特性

A linear sputtering source using electron cyclotron resonance (ECR) plasma was developed for reactive sputter deposition with large area. It is composed of slot antennas on a rectangular waveguide with 268 mm long, permanent magnets around the slots and a target within the discharge chamber. Microwaves of 2.45 GHz are radiated from the slots and generated plasma along the waveguide. A sputtering target is placed within the discharge chamber to achieve high deposition rate. Moreover, this plasma source prevents microwave window contamination by sputtered particles. The spatial uniformity of Ar plasma at 0.146 Pa was ± 7.8% within 180 mm in the long direction. By using Ti target and mixture of Ar and N2 gases, TiN films were successfully deposited with thickness uniformity of ± 11.3% within 160 mm and deposition rate of 16.2 nm/min.

Development of groove recognition algorithm with visual sensor. Practical development of visual sensor for welding robot (1st Report)

Summary To improve the automation or artificial intelligence of welding operations, it is necessary to develop high-performance sensors. Laser visual sensors are designed to recognise the configuration or detect the position of a weld by irradiating a slit light on to the welded joint, receiving the light with a CCD camera, and converting the two-dimensional information into three-dimensional information by image processing. The visual sensors for welding robots must be free from the influences of welding process disturbances, such as arc light, heat, spatter and fume. This paper describes optical component arrangements and image processing algorithms. The optical component of a sensor head helps avoid optical window contamination caused by spatter or fume. The image processor used can process image data quickly and accurately even if welding arc light illuminates the workpiece surface. The accuracy of weld position detection is within ±0.2 mm.

A curved crystal spectrometer for energy calibration and spectral characterization of mammographic x-ray sources.

Clinical efficacy of diagnostic radiology for mammographic examinations is critically dependent on source characteristics, detection efficiency, image resolution and applied high voltage. In this report we focus on means for evaluation of source-dependent issues including noninvasive determination of the applied high voltage, and characterization of intrinsic spectral distributions which in turn reflect the effects of added filtration and target and window contamination. It is shown that a particular form of x-ray curved crystal spectrometry with electronic imaging can serve to determine all relevant parameters within the confines of a standard clinical exposure.

A Two-Path, Two-Wavelength Ultraviolet Hygrometer

An ultraviolet-absorption hygrometer for airborne use was designed and tested. Here the principles of operation, the design, and the results of the first test flights are presented. The motivation for the new design is to overcome the shortcomings of existing Lyman-α devices. To solve the problem of source drift, a second optical path is employed as a reference. To address the problem of window contamination, a second ultraviolet wavelength is used. In addition, detector offsets are measured and subtracted from the signals. The flight data clearly demonstrate the value of both the reference detector and the second wavelength.

Acoustically modulated optical transmission for low level gaseous species measurement

A new optical technique has been developed for low level optical extinction measurements in gaseous media. It is a variation on direct light transmission where the sample gas density in a cell is modulated acoustically by a loudspeaker. The amplitude variation of the light transmission is proportional to the gas density and is insensitive to window contamination and detector instabilities. Preliminary analysis and experiments indicate tat the instrument promises to measure light absorption to < 1%/m. The technique has been demonstrated through the use of an absorbing gas, namely, 200 ppm of NO(2) in N(2) which produces 2.5% absorption over the observed path length of 10 cm.